My nephew is 3 1/2 and has walked on his toes since he could walk. He can walk flat foot, but doesn't normally. He has mitochondrial disease, as a result has mild autism, which they associate the tiptoeing with...which is new to me! I knew a few kids growing that did that until at least middle school! I think they eventually just outgrew it, as I know one didn't wear a brace and just made a mental effort as an older kid to quit.